This invention relates to a well structure and, more particularly, to a well structure suitable for use as a relatively shallow well of a large diameter.
A shallow well which reaches a shallow underground layer where water is gathered but not down to a deeper layer which is impervious to water is constructed in such a manner that, as shown in FIG. 7, a well curb 1 made of concrete is buried under the ground 2 and macadam 3 is laid under the well curb 1. Holes constituting a water intake 5 are formed in a portion of the well curb 1 corresponding in position to a layer 4 where water is gathered whereby underground water is taken into the well curb 1 through the water intake 5 and also through the macadam 3.
In such a conventional shallow well, if the water intake 5 is made large with a view to improving water collecting efficiency, sand tends to flow into the well curb 1 and, besides, the strength of the well curb 1 decreases with resulting occurrence of buckling or deformation by pressure of earth. Conversely, if the strength of the well curb 1 is to be sufficiently large to prevent occurrence of such buckling or deformation, the number of holes constituting the water intake 5 must be restricted which will result in decrease in the water collecting efficiency and increase in the flow speed of water collected into the well curb 1 which results in increase of sand taken into the well curb 1. Moreover, the well curb 1 is generally set in position by suspending it from above and lowering it in a pit formed in the ground. If the well curb 1 is inclined even slightly when it has been set in position, a large pressure is applied to the well curb 1 so that the well curb 1 must be designed to withstand such pressure.
U.S. Pat. No. 4,657,079 discloses a deep well screen which can resist a large pressure applied from outside. This screen however is not suitable for use as a shallow well screen using the well curb 1 made of concrete because the weight of the well curb 1 is so large that the well screen disclosed in the above mentioned U.S. patent has not sufficient strength to support the weight of the well curb 1 and it will therefore collapse in the axial direction of the screen. Moreover, in a case where the diameter of the well is large, the area of the surface of the well to which pressure of earth is applied is so large that the structure of the deep well screen will not be strong enough for resisting such pressure of earth. It is also very difficult to manufacture such a screen of a large diameter and convey it to the location of the well and assemble it with the concrete well curb 1.
It is, therefore, an object of the invention to provide a well structure suitable for use as a shallow well of a large diameter which has a sufficient strength, is convenient for conveying and assembling, and moreover has an excellent water collecting efficiency.